docs(replay): clarify fast renderer option docs #14246

Job	Run time
Ready-to-merge gate / Missing "ready-to-merge" label	4s
detect-changes	-1s
Build ${{ matrix.rn-architecture }} android ${{ matrix.build-type }}	-1s
diff_check	-1s
Test android production REV2	-1s
Test ios production REV2	-1s
Build ${{ matrix.rn-architecture }} ios ${{ matrix.build-type }} ${{ matrix.ios-use-frameworks }}	-1s
Build legacy macos ${{ matrix.build-type }}	-1s
	-3s

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